The present invention relates to the arts of nuclear medicine and diagnostic imaging. It finds particular application in conjunction with gamma cameras, and will be described with particular reference thereto. It is to be appreciated that the present invention is amendable to single photon emission computed tomography (SPECT), whole body nuclear scans, positron emission tomography (PET), compton scattering, other diagnostic modes, and/or other like applications.
Diagnostic nuclear imaging is used to study a radionuclide distribution in a subject. Typically, one or more radiopharmaceuticals or radioisotopes are injected into a subject. The radiopharmaceuticals are commonly injected into the subject's blood stream for imaging the circulatory system or for imaging specific organs which absorb the injected radiopharmaceuticals. Gamma or scintillation camera detector heads, typically including a collimator, are placed adjacent to a surface of the subject to monitor and record emitted radiation. Often, the head is rotated or indexed around the subject to monitor the emitted radiation from a plurality of directions. The monitored radiation data from the multiplicity of directions is reconstructed into a three dimensional image representation of the radiopharmaceutical distribution within the subject.
One of the problems with this imaging technique is that photon absorption and scatter by portions of the subject between the emitting radionuclide and the camera head distort the resultant image. One solution for compensating for photon attenuation is to assume uniform photon attenuation throughout the subject. That is, the subject is assumed to be completely homogenous in terms of radiation attenuation with no distinction made for bone, soft tissue, lung, etc. This enables attenuation estimates to be made based on the surface contour of the subject. Of course, human subjects do not cause uniform radiation attenuation, especially in the chest.
In order to obtain more accurate radiation attenuation measurements, a direct measurement is made using transmission computed tomography techniques. In this technique, radiation is projected from a radiation source through the subject. Radiation that is not attenuated is received by detectors at the opposite side. The source and detectors are rotated to collect transmission data concurrently with the emission data through a multiplicity of angles. This transmission data is reconstructed into an image representation using conventional tomography algorithms. The radiation attenuation properties of the subject from the transmission computed tomography image are used to correct for radiation attenuation in the emission data.
Often, the detector heads of gamma cameras are movably mounted to a rotating gantry. Generally, they enjoy various degrees of freedom with respect to the rotating gantry, including: being movable radially toward and away from the subject; being circumferentially adjustable relative to the rotating gantry; and/or, being laterally translated in tangential directions to facilitate irising of the detector heads.
Generally, the resolution of the collimated detector deteriorates with increased distance from the face of the collimator. Thus, it is desirable to place the gamma camera as close as possible to the patient to reduce the blurring caused by the distance-dependent system response function and to minimize loss of resolution. To accomplish this, non-circular orbits are used in which the detectors closely follow the body contour. To prevent possible injury, a peanut or oval contour is desired so that the detector heads avoid contact with the subject while remaining as close as possible. Moreover, accurate subject contour information improves reconstruction.
Various proximity, boundary, and/or contour determining techniques have been developed to address these issues. Generally, these techniques employ additional costly and/or cumbersome hardware that is fitted to the gamma camera. In some instances, the hardware employed is light sources and detectors to sense a break in the transmission of the light from the source to the detector caused by an interruption from an edge of the subject. However, in addition to the extra hardware employed, these techniques may be unreliable due to interference from ambient sun light.
The present invention contemplates a new and improved autocontouring device which overcomes the above-referenced problems and others.